Method and apparatus for evaluating quantities of absorbed impurities

ABSTRACT

A method and device for evaluating the quantities of adsorbed impurities in sample gas of ultra-high purity for various kinds of materials. After inert gas of ultra-high purity is supplied to a sample-gas pipe(16) through a purifier(1)(a first gas-supply source), the inside of said sample-gas pipe(16) is baked by heater(19 to 20)(heating means). The inside of sample-gas pipe(16) is kept in an atmosphere at specified temperature and then changeover valves(9, 10) are changed over from opening to closing or vice versa so that the sample gas of a specified concentration is supplied from a bomb(6)(a second gas-supply source)into the sample-gas pipe(16) until the quantities of adsorbed impurities reach saturation, in other words, from the time when, sample gas flows into the pipe to that when a microanalyzer(25) detects said gas of said specified concentration.

TECHNICAL FIELD

The present invention relates to an evaluation method and device fordetermining quantities of absorbed impurities in common gases (argongas, and the like) for use in, for example, semiconductor production,with respect to various types of materials.

BACKGROUND ART

In recent years, advances in semiconductor manufacturing technology havebeen striking, and there have been great demands for hyperfinestructures; as a result of this, it has become necessary to maintain theenvironment of the manufacturing apparatus in a state of ultrahighpurity (that is to say, purity on the level of "ppt", or parts pertrillion). As a result, in cases in which common gases of ultrahighpurity (for example, argon gas) are to be supplied through the medium ofpipes which serve as gas flow conduits, it is necessary to determine, onthe level of parts per trillion, the amount of impurities contained inthe gas, such as moisture or the like, which adhere to the inner pipesurfaces, which comprise various materials.

Examples of conventionally known methods for the detection of adsorbedamounts include, for example, a method in which a microanalyzer (anatmospheric pressure ionization mass spectrometer) is connected to thepipe end of piping which is to be tested, a gas of ultrahigh purity iscaused to flow into the piping from a gas purifier, and the amounts ofimpurities in the gas flowing out of the pipe end is measured.

However, in this conventional method, no account was taken of moisturewhich adhered to metal surfaces, and only the purity of the gas passingthrough the piping system which served as the gas conduit was measured,so that no precise determinations could be made with respect to thequality of the interior surfaces of the gas system.

The present invention was created in light of the abovedescribedproblems in the conventional technology; it has as an object thereof toprovide an evaluation method and an evaluation device for quantities ofabsorbed impurities which are capable of evaluating, on the order ofparts per trillion, quantities of impurities contained in a gas whichadsorb to a gas conduit comprising various materials.

DISCLOSURE OF THE INVENTION

In order to attain the above object, the present invention contemplatesa method wherein in a first step an inert gas of ultrahigh purity iscaused to flow into a sample-gas pipe; in a second step, the interior ofthis sample-gas pipe is baked to reach at least the level of backgroundpurity; in a third step, the interior of this sample gas pipe is placedin an atmosphere having a specified temperature; in a fourth step, theinflow of a sample gas having a specified concentration into the samplegas pipe is initiated; and in a fifth step when the quantities ofimpurities within the sample gas which adsorb to the inner surface ofthe sample gas pipe reach saturation, the inflow of the sample gas ischanged to the inflow of an inert gas.

In this case, it is preferable for the evaluation of adsorbed impuritiesthat the sample gas pipe be freely replaceable with pipes comprisingvarious materials, or the inner surfaces of which have been subjected tovarious types of processing.

Furthermore, it is preferable that the inert gas and sample gas compriseargon gas.

In order to carry out the method of the present invention, it ispreferable that the inventive apparatus be provided with: a first gassupply source, for supplying an inert gas of ultrahigh purity, a secondgas supply source, for supplying a sample gas, the added impurityamounts of which are freely adjustable, through the medium of a gas flowcontrol meter; change-over valves, which are capable of freely selectedchange-over in order to cause either an inert gas or a sample gas toflow into the sample gas pipe, and which are connected to one endopening of the sample gas pipe; a support mechanism, for supporting thesample gas pipe; a microanalyzer, which is connected to the other endopening of the sample gas pipe; and a heating mechanism, which iscapable of maintaining the interior of the sample gas pipe at a freelyselected specified temperature.

In this case, it is preferable that the inert gas and the sample gas bepassed through parts in contact with gas, the discharge gases of whichare regulated so as to at least not worsen the highest purity level ofeach gas.

Furthermore, it is preferable that the microanalyzer comprise anatmospheric ionization mass spectrometer.

FUNCTION

First, by causing a gas of ultrahigh purity (that is to say, argon gas,or the like, having a purity of parts per trillion) to flow within asample gas pipe which is to be the subject of evaluation, the interiorof this sample gas pipe is placed in an atmosphere having a specifiedhigh level of purity. Next, a heating mechanism is brought intooperation, and the interior of the sample gas pipe is baked at aspecified high temperature so as to bring the atmosphere therein to atleast a background level of purity. By means of this, the impuritieswhich adhere to the inner walls of the sample gas pipe are caused todesorb. Next, the heating mechanism is controlled so as to bring theatmosphere within the sample gas pipe to a specified temperature. Afterthis, a sample gas having a specified impurity concentration level iscaused to flow into the sample gas pipe at a specified flow rate, andthis gas is caused to flow into the sample gas pipe until the adsorbedimpurities reach saturation. When saturation has been reached, theinflow of the sample gas is halted, baking is conducted by means of theheating mechanism so as to bring the interior of the sample gas pipe toan ultrahigh purity level, and the impurities which desorb from thesample gas pipe are detected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a gas flow diagram showing an example of a device forexecuting the evaluation method in accordance with the presentinvention.

FIG. 2 is a graph showing the results of measurement by means of thedevice shown in FIG. 1.

Description of the References

1 gas purifier (first gas supply source)

6 bomb (second gas supply source)

9, 10, 11 first, second, and third valves (change-over valves)

15, 17 first and second joints (support mechanisms)

16 sample-gas pipe

25 APIMS (microanalyzer)

19, 20, 21 heaters (heating mechanisms)

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows an example of a device for executing the evaluation methodin accordance with the present invention. As shown in the figure, asupply source (not depicted in the figure) for a source gas which is aninert gas such as argon or the like, is connected to the gas inflow sideof purifier 1 through the medium of gas joint 1a, and first throughthird gas supply lines 2-4 are connected to the gas blow-off sidethereof.

A first gas flow control meter (MFC) 5 is connected to the first gassupply line 2, and bomb 6, regulator 7, and a second MFC 8 are connectedto the second gas supply line 3 in that order from the upstream side asa supply source for moisture, which constitutes an impurity.Furthermore, a first valve 9 is connected to the third gas supply line4, a second valve 10 and a third valve 11 are connected to thedownstream side of the first and second MFCs 5 and 8, and a fourth valve12 is connected to the downstream side of third valve 11.

A fifth valve 13 is provided on bomb 6, and this fifth valve 13 isconnected to the upstream side of regulator 7, and is connected on theupstream side of regulator 7 along second gas supply line 3.

Here, by providing purifier 6, argon gas of ultrahigh purity (whereinthe moisture concentration is, for example, on the level of at least 300ppt) is obtainable, and if bomb 6 is filled with, for example, argon gashaving a moisture concentration of 20-200 ppm, then, by means of theadjustment of regulator 7, argon gas having a freely selected moistureconcentration (for example, 300 ppt-1500 ppb) is obtainable at theconflux portion of the first gas supply line 2 and the second gas supplyline 3.

The first, second, and third valves, 9, 10, and 11 form an integratedchange-over valve; the opening and closing of the first and third valves9 and 11, and the second valve 10, is conducted exclusively.Furthermore, the first and second valves 9 and 10 are connected to oneend of sample gas pipe 16 through the medium of a first joint 15, whichcomprises a support mechanism, and the other end of sample-gas pipe 16is coupled with a transfer pipe 18 through the medium of a second joint17, which forms another support mechanism. Furthermore, an appropriatenumber of heaters 19-21 are attached to the sample pipe 16 in thelongitudinal direction thereof and are disposed by zone, and each heater19-21 is capable of accurately controlling the temperature of theatmosphere of the sample gas pipe 16 within the corresponding zone.Furthermore, temperature detectors 22-24 for controlling the temperatureare provided at each zone.

An atmospheric pressure ionization mass spectrometer (APIMS) 25 isconnected to the transfer pipe 18 as a microanalyzer, and an exhaustmechanism is connected to the detection portion of APIMS 25 through themedium of a flow meter 26.

An exhaust mechanism is connected to a fourth valve 12, and a smallheater 27 is attached to transfer pipe 18. Furthermore, the dischargegases of the portions in contact with gas, such as the valves 9, 10, and11, and the gas joints, are regulated so as not to reduce the purity ofthe gases which pass therethrough.

Next, an evaluation method in accordance with the present exampleconstructed in the above manner will be explained.

First, the sample-gas pipe 16, which is subject of the evaluation,comprises a stainless steel pipe, having, for example, a pipe diameterof 1/4 inches (1 inch=2.45 cm) and a pipe length of 2 meters, andfurthermore, the inner surface thereof has been subjected toelectrolytic polishing, and furthermore, an oxide layer has been formedthereon, and this is placed between joints 15 and 17.

Next, the second valve 10 is closed, and the first valve 9 and thethird-sixth valves 11-14 are opened, and the first and third gas supplylines 2 and 4, and sample-gas pipe 16 is purged by means of argon gas ofultrahigh purity. After this, heaters 19-21 are controlled so as toplace the interior of sample-gas pipe 16 in an atmosphere having a hightemperature, for example, 450° C.; that is to say, baking is conducted.

In this case, the first valve 9 is open, and the second valve 10 isclosed, so that argon gas of ultrahigh purity (the moistureconcentration thereof being, for example, of at least a level of 300ppt) is caused to flow into sample-gas pipe 16 through the medium offirst gas supply line 2.

Furthermore, at this time, the third and fourth valves 11 and 12, aswell as the fifth and sixth valves 13 and 14 are opened, so that argongas adjusted to a specified moisture concentration is blown off by meansof an exhaust mechanism through the medium of second gas supply line 3and third gas supply line 4. That is to say, argon gas having thismoisture concentration can be supplied to sample-gas pipe 16 at aspecified flow rate (for example, 1.2 liter/min). The adjustmentnecessary to provide the specified flow rate is conducted by means offirst and second MFCs 5 and 8.

Baking is conducted until the interior of sample-gas pipe 16 reaches atleast a background level of purity; the confirmation as to whether ornot this level of purity has been reached is carried out by means ofAPIMS 25.

After it has been confirmed that the interior of sample-gas pipe 16 hasreached a background level of purity, heaters 19-21 are controlled basedon the output of temperature detectors 20-22 in order to cool theinterior of sample-gas pipe 16 to a desired atmospheric temperature (forexample, 23° C.). In this case, the small heater 27 is controlled sothat transfer pipe 18 is also adjusted to a specified atmospherictemperature.

Next, from the above-described open and closed state of each valve, thesecond valve 10 is opened, and the first valve 9, as well as the thirdand fourth valves 11 and 12, are closed. By means of this, argon gashaving a specified moisture concentration is caused to flow at aspecified flow rate into sample-gas pipe 16 through the medium of secondvalve 10. By means of this inflow, moisture begins to adhere to theinner walls of sample gas pipe 16, so that the inflow initiation time isrecorded.

The quantity of absorbed moisture is determined by the surface area ofthe inner wall of sample gas pipe 16, so that it reaches saturation at apredetermined amount. Accordingly, if the period of time from theinitiation of the inflow of argon gas having the specified moistureconcentration to the detection of argon gas having a specified moistureconcentration by means of APIMS 25 is calculated, the saturationadsorption amount of the moisture can be evaluated.

When the quantities of adsorbed moisture reach saturation, from theabove opened and closed states of the valves, the second valve 10 isclosed, and the first valve 9, as well as the third and fourth valves 11and 12, are opened. Then, heaters 19-21 are again controlled and bakingis conducted so that the moisture adhering to the inner surface ofsample-gas pipe 16 is desorbed.

Hereinafter, the above procedure is repeated in order to conductmeasurement at other atmospheric temperatures (for example, 40° C., 60°C., 80° C., and the like).

FIG. 2 shows the results of the moisture adsorption evaluation of thesample gas pipe by means of the above method; the vertical axisindicates a time T, while the horizontal axis indicates a moistureconcentration C within the sample gas (argon gas). That is to say, thepoint in time at which the moisture adsorption reaches saturation isapproximately coincident with the point in time at which theconcentration Cm of the argon gas which is caused to flow in isconfirmed at the end of sample-gas pipe 16. Furthermore, it can be seenthat as the atmospheric temperature within sample-gas pipe 16 increases,the time which elapses before adsorption saturation occurs becomesshorter.

By altering the materials or the inner surface processing method (filmmaterial or the like) of the sample-gas pipe 16, it is possible toconduct an evaluation of the moisture adsorption (the process isidentical with respect to other impurities as well) with respect tovarious materials in an ultrahigh purity region.

INDUSTRIAL APPLICABILITY

In accordance with the invention, a first step, in which a inert gas ofultrahigh purity is caused to flow into a sample-gas pipe; a secondstep, in which the interior of the sample-gas pipe is baked so as toreach at least background purity level; a third step, in which theinterior of the sample-gas pipe is set to a specified atmospherictemperature; a fourth step, in which the inflow of a sample gas having aspecified concentration into the sample-gas pipe at a specified flowrate is initiated; and a fifth step, in which, when the quantity ofimpurities within the sample gas adsorbing to the inner surface of thesample-gas pipe reaches saturation, the inflow of the sample gas isswitched to the inflow of an inert gas, are provided, so that it ispossible to easily conduct the evaluation of impurity adsorption amountsat an ultrahigh purity level with respect to specified materials, and itis thus possible to contribute, in particular, to the manufacture ofsemiconductors having hyperfine structures.

Furthermore, in accordance with the invention, it is possible to easilyconduct impurity evaluation with respect to various sample-gas pipes tobe evaluated by means of the exchange of sample-gas pipes.

Furthermore, in accordance with the invention, it is possible toconcomitantly use both a sample gas and a carrier gas for purging, andfurthermore, measurement and handling is facilitated, as argon gas isphysically and chemically stable.

What is claimed is:
 1. A method for evaluating quantities of adsorbedimpurities, the method comprising:a first step, in which an inert gas ofultra-high purity is caused to flow into a sample-gas pipe, a secondstep, in which an interior of said sample-gas pipe is baked to reach atleast a level of background purity, a third step, in which said interiorof said sample-gas pipe is placed in an atmosphere having a specifiedtemperature, a fourth step, in which an inflow of a sample gas having aspecified concentration into said sample-gas pipe is initiated, and afifth step, in which, when quantities of impurities within said samplegas which adsorb to an inner surface of said sample-gas pipe reachsaturation, said inflow of said sample gas is changed to an inflow of aninert gas.
 2. A method for evaluating quantities of adsorbed impuritiesin accordance with claim 1, further comprising a step of exchanging saidsample-gas pipe for sample-gas pipes made of various materials, andwhose inner surfaces have been subjected to various types of processing.3. A method for evaluating quantities of adsorbed impurities inaccordance with claim 2, wherein the various materials for saidsample-gas pipes are stainless steel, aluminum, or glass.
 4. A methodfor evaluating quantities of adsorbed impurities in accordance withclaim 2, wherein the inner surface of said sample-gas pipe has beensubjected to electrolytic polishing, and has an oxide layer formedthereon.
 5. A method for evaluating quantities of adsorbed impurities inaccordance with claim 1, wherein said inert gas and said sample gascomprise argon gas.
 6. A method for evaluating quantities of adsorbedimpurities in accordance with claim 5, wherein said argon gas has amoisture concentration of 1500 ppb or below.
 7. An apparatus forevaluating quantities of adsorbed impurities, the apparatus comprising:asample gas pipe formed from materials which have a known affinity foradsorbing impurities from a sample gas flowing therethrough, a first gassupply source, for supplying an inert gas of ultrahigh purity, a secondgas supply source, for supplying a sample gas, added impurity amounts ofwhich are freely adjustable, through the medium of a gas flow controlmeter, change-over valves, which are capable of freely selectedchange-over in order to prevent either said inert gas or said sample gasfrom flowing into the sample-gas pipe, and which are connected to oneend opening of said sample-gas pipe, support means for supporting saidsample-gas pipe, a microanalyzer for analyzing gas impurities in a gasflow, said microanalyzer being connected to another end opening of saidsample-gas pipe, and heating means for maintaining an interior of saidsample-gas pipe at a freely selected specified temperature.
 8. Anapparatus for evaluating quantities of adsorbed impurities in accordancewith claim 7, further comprising means for passing said inert gas andsaid sample gas through impurity adsorber parts in contact with gas, andmeans for regulating discharge gases to an extent such that a puritylevel of each said gas is at least not caused to decline.
 9. Anapparatus for evaluating quantities of adsorbed impurities in accordancewith claim 8, wherein said parts in contact with gas are made of thesame material as that of said sample-gas pipe.
 10. An apparatus forevaluating quantities of adsorbed impurities in accordance with claim 7,wherein said microanalyzer includes an atmospheric pressure ionizationmass spectrometer.
 11. An apparatus for evaluating quantities ofadsorbed impurities in accordance with claim 7, wherein said heatingmeans include an appropriate number of heaters which are attached tosaid sample-gas pipe and spaced apart in a longitudinal directionthereof, and each of said heaters includes means for individuallycontrolling the temperature.
 12. An apparatus for evaluating quantitiesof adsorbed impurities in accordance with claim 7, wherein saidsample-gas pipe and said microanalyzer are connected by a transfer pipe,and wherein said heating means include an appropriate number of heaterswhich are attached to said transfer pipe and spaced apart in alongitudinal direction thereof.